The invention relates to railroad vehicles having axles with metal support wheels and it finds a particularly suitable for use in the construction of high speed transport installations whose track includes urban sections likely to comprise small radius curves.
Conventional railroad axles are self guided because the two wheels are interlocked for rotation and have tapered treads so that any offcentering of the axle causes the radii of the rolling circles on both sides of the axle to vary in opposite directions. The axle then tends to move in a direction which recenters it with respect to the track. To avoid any instability, two axles in a bogey are connected by means of resilient return means in the axle boxes, optimization being obtained by an appropriate choice of the stiffness of the return means, of the wheel base, of the taper of the tread and of the unsuspended weights.
But the search for high speed stability leads to choosing, for the stiffness of the resilient return means, the wheel base of the bogey and the taper of the treads, values which reduce the possibility of passing without slipping over highly curved track sections in practice, for the values chosen at present, it is not possible to negociate a radius of about 700 m without the risk of the wheels coming into contact by their flanges. At the present time, in order to be able to negociate the inevitable curves in an urban environment, it is necessary to grease the rails for high speed equipment.
Different approaches have been proposed to make high speed stability and the negociation of tight curves compatible. One approach, used with the Spanish "TALGO" trains, consists in using an axle with independent wheels oriented by a shaft hitched to the preceding carriage of the train. The device makes the trains irreversible, does not operate on the leading carriage and does not provide accurate guiding on going into and leaving curves. These are troublesome limitations.